Movie Alien Attacks

What is the number one rule when it comes to war?  The guys with the better weapons and technology win.  Why do you think that when the US invaded Iraq we routed them in a couple of weeks with very few casualties?  It's because America's war machine was vastly better than the other guy's.  So, why is it that when the technologically superior aliens attack Earth in a movie the Earth is somehow able to win?  There is no way that humans should stand a chance against a species that was able to travel light-years across the universe in order to wipe out our puny butts.  And yet, Hollywood always comes up with some sort of stupid reason that the aliens lose.  Just look at these movies and the illogical Achilles Heel that they give their aliens:

• War of the Worlds - The Common Cold.  This one kind of makes sense except that we know the aleins have been to Earth before and they probably would have come across the common cold and figured out a way to protect themselves from it by the time they attack.
• Mars Attacks! - Crappy Music.  Okay, this one was a comedy and gets a pass.
• Killer Klowns from Outer Space - A Police Badge.  Remember this movie?  It was so bad, it was awesome.  Oh, and the humans win when one of them pokes the head clown's nose with the sharp point of his police badge and explodes somehow.  Ridiculous.
• Cowboys & Aliens - Incompetence.  I've covered this one before.
• Battle: Los Angeles - Terrible Security.  If you didn't see this movie, I don't blame you, it was terrible.  But the humans win because they were able to sneak up on the aliens' main spaceship and blow it up and the aliens took to long to respond because no one bothered to have a couple of guys keeping a lookout.
• The Faculty - Homemade Drugs.  I don't know, I saw this a long time ago and I think the humans won because the druggie character of the group used his drugs on the aliens which killed them.
• Signs - Water.  This weakness was beyond stupid.  I'm fairly sure that all lifeforms in the universe need water to live and somehow M. Night Shamalamadingdong thinks it would be his aliens' biggest weakness.  So dumb.
• Independence Day - A Computer Virus (and Randy Quaid).  In all honesty, this one isn't even worth going into, but a computer virus?  Really?!?  It takes quite a bit of time to write the code for a virus for Earth's computers, but the guy from Jurassic Park was able to make one for alien software in a couple of hours.  Bullshit.

As you can see, only one of those alien weaknesses could even be considered legitimate and even that one could have been avoided with a simple surgical mask.  Come on, Hollywood, I know you love to make movies where the underdog wins, but Earth isn't even an underdog when it goes up against aliens, they are more like under-ants just waiting to get stepped on.

"I always laugh when I see one of these little guy's heads explode."